Grey pictures in my pictures folder

I'm trying to find an answer for my problem and can't find any solutions so let's try here and see

I have a folder with pictures in it, one of the picture is showing correctly but the other ones are grey. If I click on a grey picture I will see it without any problems.

What can I do to have my other pictures showing correctly in that folder, I didn't installed any new software or neither change any configurations in my computer so I don't know what is happening there.

I have another folder with pictures and it was doing the samething, I copied them back into the folder and it was allright. It seems strange to me that suddenly all my pictures are changing from normal view to kind of grey look....

Make another folder, cut and paste the pictures in to there (now they should be fine)

Delete the old folder and rename the new one as the last one.

i.e.

1. I had a folder called 'New'
2. I then created a folder called 'New1'
3. I then Cut and pasted the pictures from 'New' to 'New1' one.
4. Deleted the empty 'New' folder and renamed 'New1' back to
New!

Thanks robin.munro, I did that and everything is allright now but I'm still curious about what causes that to happen to all my files with pictures in it so pls if you ever have an answer for that one feel free to post it....